1. Field of the Invention
The present disclosure relates generally to communication systems, and more specifically to a technique for correcting carrier frequency offset in multi-carrier communication systems.
2. Related Art
Multi-carrier communication (MC) techniques are often used both in wire-line and wireless telecommunication systems to transmit multiple streams of symbols, with each symbol typically containing one or more bits. In a MC system, a transmission band/channel is divided into a number of narrow bandwidth sub-channels, and in a transmitter device in a MC system each stream of symbols may be modulated on a corresponding sub-channel carrier signal.
Generally each sub-channel carrier signal is modulated (using techniques such as Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (QAM), etc., well known in the relevant arts) to encode the corresponding stream of symbols. The resulting sub-channel signals may be added together to generate a single base-band multi-carrier signal, by techniques such as inverse discrete Fourier transform (IDFT) or inverse fast Fourier transform (IFFT). The base-band multi-carrier signal may then be shifted (commonly referred to as upconversion) to a desired higher frequency band suitable for transmission using a high frequency carrier signal.
A receiver device obtains the base-band multi-carrier signal by shifting the higher frequency band signal back to the base-band frequency (commonly referred to as “down conversion”). The stream of symbols encoded in each sub-channel is derived from the base-band signal by using transform techniques such as DFT, FFT, etc. The data corresponding to each symbol is then recovered by suitably demodulating (based on the modulation technique adapted at the transmitter system) the corresponding sub-channel carrier signal.
Typically, at the receiver device, the down conversion (shifting of high frequency signal to base band signal) is performed using a locally generated carrier signal having a frequency value equal to the high frequency carrier signal used at the transmitter device. The difference in frequency value of locally generated carrier signal and carrier of the received signal (which may be due to oscillator frequency drift, Doppler effects, etc., well known in the relevant arts) is generally referred to as a carrier frequency offset.
One general requirement for accurate recovery of data using MC techniques is that the frequency of the locally generated carrier signal used in the receiver device, needs to equal the frequency of the signal transmitted. In other words, the carrier frequency offset needs to ideally equal zero.
When the offset deviates from the ideal zero, data bits from a multi-carrier system may not be recovered accurately. Such a problem is of particular concern in telecommunication systems using Orthogonal Frequency Division Multiplexing (OFDM) techniques or Discrete Multi-tone Techniques (DMT) due to the overlap of the sub-channel frequencies, and effects of inter-channel interference (ICI) that may be caused due to carrier frequency offsets.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.